1. Field of the Invention
The present invention relates to a toner resin composition for use in electrophotography or the like, and further to a toner prepared from the resin composition. More particularly, the present invention relates to a toner resin composition for use in a so-called dry development, one of methods which develop electrostatic latent images, and further to a toner prepared from the resin composition.
2. Description of Related Art
In an electrophotographic or similar field, the dry development has been widely used as one of the methods which develop electrostatic latent images. In the dry development process, toners are generally charged through frictional contact with so-called carriers such as iron particles or glass beads. The charged toners are then electrically attracted by and deposited on the electrostatic latent images produced on an electroreceptor. The produced toner images are transferred onto a paper and then fixed thereon, as by a heat roll, so that visual images are permanently provided.
For fixation of the toner images, a heat roll method is a popular choice which utilizes a heat roll having a surface coated with a substance that shows a release property relative to the toners. A paper onto which the toner images have been transferred is compressed against the heat roll so that they are thermally fixed on the paper.
In order to improve a process economy, e.g., reduction in power consumption, as well as to increase a copying speed, a toner resin for particular use in the heat roll method has been sought which can be fixed at temperatures lower than conventionally employed.
Also in the heat roll fixation method, a toner while in a molten state is compressively brought into contact with the heat roll surface. This results in the increased tendency for a portion of the toner to adhere to the heat roll surface from which the adhered toner portion is retransferred onto a subsequently-introduced paper, i.e., the increased occurrence of a so-called offset phenomenon.
One technique to restrain the occurrence of this offset phenomenon is the provision of a release coating, e.g., a silicone oil coating on the heat roll surface. This technique, however, problematically requires complex procedures and facilities for providing the release coating. A need has accordingly arisen for a toner resin which is excellent in offset resistance. The term "offset resistance", as used herein, refers to a toner property by which the offset phenomenon can be maintained at a reduced degree of occurrence.
A method to improve the offset resistance has been proposed, for example, in Japanese Patent Publication No. 52-3304 (1977) which utilizes a low molecular weight polypropylene as a release agent for inclusion in toners. While the inclusion of a release wax, such as polypropylene, in toners is certainly effective in enhancing the offset resistance, the use of polypropylene having a higher melting point undesirably leads to reduced fixability of the toners.
In an attempt to improve both fixability and offset resistance, toners have been proposed which contain a low molecular weight or low viscosity ethylene-based wax, for example, by Japanese Patent Laying-Open Nos. 07-36218 (1995) and 08-114942 (1996). In general, the inclusion of a wax in a toner not only improves its release property, but also results in a reduced occurrence of DF (document feeder) staining. However, the current state of the art has not yet reached to a satisfactorily effective level.